The crystal structure of WS2 is similar to that of MoS2, which is a hexagonal close-packed layered structure. There is a strong chemical bond connection between the W atom and the S atom, while the interlayer S atoms are connected to each other by a weak molecular bond. The banding force between layers is a van der Waals force, and the interlayer spacing of WS2 is larger than that of MoS2. The thermal stability of WS2 is also better. The WS2 decomposes at 510° C., is oxidized fast at 539° C. in the atmosphere, and decomposes at 1150° C. in vacuum. Therefore, it can be used in a harsh application environment such as high temperature, high pressure, high vacuum, high load, radiation, and corrosive media.
As an electrode material for lithium ion batteries and sodium ion batteries, WS2 has attracted extensive concerns. At present, the methods for the preparation of WS2 materials mainly comprise: a thermal decomposition method [ZHU Ya-jun, ZHANG Xue-bin, JI Yi, et al. Preparation Technology and Applications of Nanoscaled WS2 and MoS2 [J]. Guangzhou Chemical Industry, 2012, 3(40): 4-6.], a solid-gas sulfuration method [Yan-Hui Li, Yi Min Zhao, Ren Zhi Ma, Yan Qiu Zhu, Niles Fisher, Yi Zhang Jin, Xin Ping Zhang. Novel Route to WOx Nanorods and WS2 Nanotubes from WS2 Inorganic Fullerenes [J]. J. Phys. Chem. B. 2006, 110: 18191-18195.], an in-situ evaporation synthesis method [A Margolin, F L Deepak, R Popovitz-Biro, M Bar-Sadanl, Y Feldman, R Tenne. Fullerene-like WS2 nanoparticles and nanotubes by the vapor-phase synthesis of WCln and H2S [J]. Nanotechnology. 2008, 19:95601-95611.], a spraying pyrolysis method [Seung Ho Choi, Yun Chan Kang. Sodium ion storage properties of WS2-decorated three-dimensional reduced graphene oxide microspheres [J]. Nanoscale. 2015, 7: 3965-3970], a precipitation reduction method [ZHENG Yi-Fan, SONG Xu-Chun, LIU Bo, HAN Gui, XUZhu-De. Preparation and Mechanism of Nesting Spherical Layered Closed-cage Structured Nano WS2 [J].Journal of Inorganic Materials, 2004, 3(19): 653-656.], and a chemical vapor deposition (CVD) method [Arunvinay Prabakaran, Frank Dillon, Jodie Melbourne, et al. WS2 2D nanosheets in 3D nanoflowers[J]. Chem. Commun. 2014, 50: 12360-12362]. In addition, a WS2-graphene anode composite material for a sodium ion battery has been prepared using a hydrothermal method [Dawei Su, Shixue Dou, Guoxiu Wang. WS2@graphene nanocomposites as Anode Materials for Na-Ion Batteries with Enhanced Electrochemical Performances[J]. Chem. Comm., 2014, 50: 4192-4195.], and a WS2/MoS2 composite has been prepared by an ultrasonic ball milling method [MAO Daheng, SHI Chen, MAO Xianghui, MAO Yan, LI Dengling. Method for Preparing Nano WS2/MoS2 Granules [P]. ZL 201010200269.6].
Meanwhile, tungsten trioxide (WO3) is a significant functional material as it is the most stable oxide of tungsten at room temperature, environmentally friendly, low-cost, and of high theoretical capacity (693 mAh·g−1), thus being a promising anode material for lithium ion batteries. However, because of the low conductivity and the large volume change during the charging and discharging process, bulk WO3 has a poor rate capability and a poor cycle stability. Therefore, in order to improve the lithium storage dynamic properties of WO3 materials, controlling the synthesis of WO3 nanomaterials with various morphologies is considered as one improvement method. At present, the related studies reported on the WO3 nanomaterials comprise: preparation of WO3 nanoparticles by Microemulsion Method [Hou Changjun, Diao Xianzhen, Tang Yike, Huo Danqun, Wei Linfan. Synthesis and Characterization of WO3 Nano-Powder Based on Micro-Reactor in Microemulsion System [J]. RARE METAL MATERIALS AND ENGINEERING, 2007, 36 (3): 60-63]; preparation of WO3 nanocrystalline materials by a hydrothermal method [Tianming Li, Wen Zeng, Bin Miao, Shuoqing Zhao, Yanqiong Li, He Zhang. Urchinlike hex-WO3 microspheres: Hydrothermal synthesis and gas-sensing properties [J]. Materials Letters, 2015, 144: 106-109]; preparation of six spline spherical WO3 by a hydrothermal method [Li Jiayin, Huang Jianfeng, Wu Jianpeng, Cao Liyun, Kazumichi Yanagisawa. Morphology-controlled synthesis of tungsten oxide hydrates crystallites via a facile, additive-free hydrothermal process[J]. Ceramics International, 2012, 38: 4495-4500]; preparation of nano WO3 with tungsten powder and hydrogen peroxide-peroxide poly-tungstic acid method [YE Ai-ling, HE Yun-qiu. Photochemical and electrochemical properties of tungsten trioxides and tungsten trioxide hydrates [J]. JOURNAL OF FUNCTIONAL MATERIALS, 2014, 12 (45): 12042-12046] and [HUANG Jianfeng, LI Jiayin, CAO Liyun, HU Baoyun, WU Jianpeng. Preparation method of hexagon snow shaped WO3 nanometer disc [P]. ZL 200910218869.2]; preparation of hollow mesoporous WO3 spheres by a spray drying-heat treatment [LIU Bai-Xiong, WANG Jin-Shu, LI Hong-Yi, WU Jun-Shu, LI Zhi-Fei. Hollow Mesoporous WO3 Spheres: Preparation and Photocatalytic Activity [J]. Chinese Journal of Inorganic Chemistry, 2012, 28 (3): 465-470]; an acidification precipitation method [Chong Wang, Xin Li, Changhao Feng, Yanfeng Sun, Geyu L. Nanosheets assembled hierarchical flower-like WO3 nanostructures: Synthesis, characterization and their gas sensing properties [J]. Sensors and Actuators B, 2015, 210: 75-81]; and a chemical vapor deposition method (CVD) [Jianzhe Liu, Mianzeng Zhong, Jingbo Li, Anlian Pan, Xiaoli Zhu. Few-layer WO3 nanosheets for high-performance UV-photodetectors [J]. Materials Letters, 2015, 148: 184-187].
In these methods, the powders were synthesized at a high temperature in an inert atmosphere by a precipitation reduction method, a thermal decomposition method, and a sulfidation method, which are prone to agglomeration, the process conditions are difficult to control, and the utilization rate of original materials required for the preparation is much lower. In addition, according to the solid state reaction, sintering or sulfidation reaction in a reduction atmosphere can also lead to agglomeration of nanocrystals and abnormal growth of grains, thus it is difficult to tailor and control the microstructure of the materials. The in-situ evaporation method and chemical vapor deposition method have high requirements for equipment and the corresponding ratio of reactants is difficult to control. In addition, impurities are prone to be introduced into the prepared nanomaterial, and the powders are prone to agglomeration. However, there are few reports on research about WS2 and WO3 composite materials, their application as an anode material for a sodium ion battery, and a hard template assisted sol-low temperature vacuum thermal reduction technology for preparation of a WO3/WS2 porous hollow shell nanomaterial by combining a mesocarbon microbead (MCMB) assisted sol technology and a low temperature thermal reduction method.